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| Home > Publications database > Abscheidung von amorphem Silizium (a-Si:H) aus an einem heißen Blech zersetztem Silan |
| Book/Report | FZJ-2018-03673 |
1991
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/19068
Report No.: Juel-2552
Abstract: Hydrogenated amorphous silicon (a-Si:H) films were deposited from silane dissociated on metal ribbons at temperatures between 1300$^\circ$ C and 2500$^\circ$ C. The ribbon material was tungsten, some films were produced using molybdenum and tantalum. A silane flow was directed onto the ribbons and the gas pressure waskept low enough to reduce gas phase reactions. From the decomposition products a-Si:H films were formed on a subtrate holder held at temperatures between 50 °C and 500$^\circ$ C. This deposition method further allows t deposit a-Si:H based alloys with carbon or germanium by placing another hot ribbon with a separate gas supply in the vacuum. In this configuration the source gases (silane, methane, germane etc.) are decomposed separately, which is not possible with other deposition techniques. During the presented work a deposition system was designed and constructed . In this system first the deomposition of silane on the hot ribbon was investigated and second the film properies were analysed especially in the low pressure region. From the results of the first investigation it was concluded that the silane decomposition proceeds via adsorption of the gas molecules on the tungsten surface. The silane adsorbs and is decomposed to silicon and hydrogen whichsubsequently desorb seperately. At ribbon temperatures of more than 1800$^\circ$ C the silane decomposition is complete and the growth rate stays constant. The tungsten contamination of the films only depends on the tungsten vapor pressure. At a temperature of 1800$^\circ$ C this contamination is not significant. But the films which are directly formed from the particles desorbing from the hot ribbon are not suitable for opto-electronic applications because their photoconductivity is much lower than in the glow discharge films currenly used. The film properties can be improved by variation of deposition parameters which raise the silane partialpressure in the gas phase during deposition. It is concluded that the film properties are controlled by a reaction of undecomposed silane with the silicon atomsdesorbing from the hot ribbon surface. In this process hydrogen containing radicals are formed which are more mobile on the growing surface than the silicon atomsresulting in a more compact structure of the films. Additionally the question was investigated if by the same method hydrocarbons can be dissociated to produce a-Si :C:H alloys. Because of the higher chemical stability of the hydrocarbons and because of the lower vapor pressure of carbon (graphite) the ribbon temperature must be so high that the tungsten contamination of the films becomes a problem. Therefore the production of a-Si :C:H alloy films by the hot ribbon method is not as successful as in the case of a-Si:H. The presented work is in context with recent investigations on the stability of films produced in a similar way. There are indications that the degradation under illumination by light is strongly reduced in these films. These indications are also found in the presented work i. e. a more ordered structure of the hot ribbon films compared to the a-Si:H films produced by the glow discharge method. Accordingly it is recommended to continue the developement of the hot ribbon method because this probably leads to a progress in the control of the stability of a-Si:H.
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